NAME

       v.lidar.correction   -  Correction  of  the  v.lidar.growing output. It is the last of the
       three algorithms for LIDAR filtering.

KEYWORDS

       vector, LIDAR

SYNOPSIS

       v.lidar.correction
       v.lidar.correction help
       v.lidar.correction [-e] input=name  output=name  terrain=name   [sce=float]    [scn=float]
       [lambda_c=float]   [tch=float]   [tcl=float]   [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -e
           Estimate point density and distance
           Estimate  point  density  and  distance for the input vector points within the current
           region extends and quit

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Input observation vector map name (v.lidar.growing output)

       output=name
           Output classified vector map name

       terrain=name
           Only 'terrain' points output vector map

       sce=float
           Interpolation spline step value in east direction
           Default: 25

       scn=float
           Interpolation spline step value in north direction
           Default: 25

       lambda_c=float
           Regularization weight in reclassification evaluation
           Default: 1

       tch=float
           High threshold for object to terrain reclassification
           Default: 2

       tcl=float
           Low threshold for terrain to object reclassification
           Default: 1

DESCRIPTION

       v.lidar.correction is the last of three steps to filter LiDAR data.  The  filter  aims  to
       recognize  and  extract  attached  and  detached object (such as buildings, bridges, power
       lines,  trees, etc.)  in order to create a Digital Terrain Model.
       The module, which could be iterated several times, makes a comparison  between  the  LiDAR
       observations  and a bilinear spline interpolation with a Tychonov regularization parameter
       performed on the TERRAIN SINGLE PULSE points  only.  The  gradient  is  minimized  by  the
       regularization  parameter.   Analysis  of  the  residuals between the observations and the
       interpolated values results in four cases (the next classification is referred to that  of
       the v.lidar.growing output vector):
       a)  Points classified as TERRAIN differing more than a threshold value are interpreted and
       reclassified as OBJECT, for both single and double pulse points.
       b) Points classified  as  OBJECT  and  closed  enough  to  the  interpolated  surface  are
       interpreted and reclassified as TERRAIN, for both single and double pulse points.

NOTES

       The  input  should  be  the  output  of  v.lidar.growing  module  or  the  output  of this
       v.lidar.correction itself. That means, this module could be applied more times  (although,
       two  are usually enough) for a better filter solution. The outputs are a vector map with a
       final point classification as as TERRAIN SINGLE PULSE, TERRAIN DOUBLE PULSE, OBJECT SINGLE
       PULSE or OBJECT DOUBLE PULSE; and an vector map with only the points classified as TERRAIN
       SINGLE  PULSE  or  TERRAIN  DOUBLE  PULSE.   The  final  result  of  the  whole  procedure
       (v.lidar.edgedetection,    v.lidar.growing,    v.lidar.correction)   will   be   a   point
       classification in four categories:
       TERRAIN SINGLE PULSE (cat = 1, layer = 2)
       TERRAIN DOUBLE PULSE (cat = 2, layer = 2)
       OBJECT SINGLE PULSE (cat = 3, layer = 2)
       OBJECT DOUBLE PULSE (cat = 4, layer = 2)

EXAMPLES

   Basic correction procedure

       v.lidar.correction input=growing output=correction out_terrain=only_terrain

   Second correction procedure

       v.lidar.correction input=correction output=correction_bis out_terrain=only_terrain_bis

SEE ALSO

       v.lidar.edgedetection, v.lidar.growing, v.surf.bspline

AUTHORS

       Original version of program in GRASS 5.4:
       Maria Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko Reguzzoni
       Update for GRASS 6.X:
       Roberto Antolin and Gonzalo Moreno

REFERENCES

       Antolin, R. et al., 2006. Digital terrain models determination  by  LiDAR  technology:  Po
       basin experimentation. Bolletino di Geodesia e Scienze Affini, anno LXV, n. 2, pp. 69-89.
       Brovelli M. A., Cannata M., Longoni U.M., 2004. LIDAR Data Filtering and DTM Interpolation
       Within GRASS, Transactions in GIS, April 2004,  vol. 8, iss. 2, pp. 155-174(20), Blackwell
       Publishing Ltd.
       Brovelli M. A., Cannata M., 2004. Digital Terrain model reconstruction in urban areas from
       airborne laser scanning data: the method and  an   example  for  Pavia  (Northern  Italy).
       Computers and Geosciences 30 (2004) pp.325-331
       Brovelli  M.  A. and Longoni U.M., 2003. Software per il filtraggio di dati LIDAR, Rivista
       dell?Agenzia del Territorio, n. 3-2003, pp. 11-22 (ISSN 1593-2192).
       Brovelli M. A., Cannata M. and Longoni U.M., 2002. DTM LIDAR in  area  urbana,  Bollettino
       SIFET N.2, pp. 7-26.
       Performances  of the filter can be seen in the ISPRS WG III/3 Comparison of Filters report
       by Sithole, G. and Vosselman, G., 2003.

       Last changed: $Date: 2010-09-16 00:25:59 -0700 (Thu, 16 Sep 2010) $

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